Virtually all telecommunications carriers, such as AT&T, now employ fiber optic cables to carry telecommunications traffic between facilities. As compared to conventional copper cables, fiber optic cables afford much greater bandwidth and virtual immunity from cross talk and interference. Many telecommunications carriers bury their fiber optic cables underground for reasons of safety and esthetics. Several different methods exist for underground cable burial. For example, some carriers directly plow the fiber optic cable underground with no protective enclosure. Other carriers first plow a plastic duct underground and then pull the fiber optic through the duct via a rope placed in the duct prior to burial.
Regardless of the burial method, the metallic sheath of the cable must remain isolated from the earth. Any electrical contact between the sheath and ground will cause locating signals impressed on the sheath to pass to ground. Grounding the cable sheath makes detection of the locating signals very difficult using conventional electromagnetic signaling. Consequently, a technician must use other cable locating techniques that are more complicated and less reliable. For that reason, most owners of fiber optical cables demand integrity of the fiber optic cable sheath as part of the installation process. As an example, AT&T requires its fiber optic installation contractors to measure the resistance between the cable sheath and ground following installation. If the resistance exceeds 25,000 Ohms (25 K ohms), then a cable sheath fault exists which the contractor must repair.
In practice, locating sheath faults has proven difficult especially in a long cable run. For that reason, many cable installation contractors will ignore sheath faults during installation. Consequently, such sheath faults will remain, and potentially worsen.
Thus, there is need for a technique for detecting fiber optic cable sheath faults during installation.